Percussive electronic musical instrument with output level controlled by intensity of key depression

ABSTRACT

A unit for controlling the output level of a tone generator of an electronic musical instrument according to the intensity with which a key of the instrument is depressed. A diode used in its nonlinear range is employed in the unit for graduating a normally abrupt change between time constants of the output waveform of the unit.

United States Patent 72] Inventors Popko Reinder Dijksterhuis Deceased,

Late of Bilthoven; Casper Antonius Henricus Mulkens, Administrator, Eindhoven, Netherlands [2]] Appl. No. 759,532

[22] Filed Sept. 12, 1968 [45] Patented Mar. 2, 1971 [73] Assignee U.S. Philips Corporation New York, N.Y.

[32] Priority Sept. 15, 1967 [3 3 Netherlands [54] PERCUSSIVE ELECTRONIC MUSICAL INSTRUMENT WITH OUTPUT LEVEL CONTROLLED BY INTENSITY OF KEY DEPRESSION 5 Claims, 7 Drawing Figs.

[52] U.S. Cl 84/1-26, 84/1.1 [51] Int. Cl. Gl0h l/02 Primary Examiner Milton O. Hirshfield Assistant Examiner-Stanley, J. Witkowski Att0rneyF rank R. Trifari ABSTRACT: A unit for controlling the output level of a tone generator of an electronic musical instrument according to the intensity with which a key of the instrument is depressed. A diode used in its nonlinear range is employed in the unit for graduating a normally abrupt change between time constants of the output waveform of the unit.

PATENTEI] MAR 219w T I 25- I I INVENTOR. POPKO REINDER DIJKSTERHUIS, DECEASED,

By CASPER ANTONIUS HENRICUS MULKENS, ADMINISTRATOR. BY

- ENT PERCUSSIVE ELECTRONIC MUSICAL INSTRUMENT WITII OU'IIUT LEVEL CONTROLLED BY INTENSITY OF KEY DEPRESSION The invention relates to an electronic musical instrument, in which oscillations produced by tone generators are supplied to a member which transmits these oscillations only if upon actuation of a key a voltage derived from a capacitor is impressed on it, the value of the voltage depending upon the intensity of the actuation which voltage then decreases again to zero through a discharge circuit.

In such instruments, particularly those for the imitation of string instruments such as, for example, harpsichords, pianos and the like, steps should be taken to ensure that with rapid repetitions the separate actuations are still audible. This cannot be achieved without further expedients with one capacitor, because the time constant of the discharge circuit is so small that the tone decays too rapidly or is so large that after one strong actuation followed by'rapid weak repetitions the capacitor still has a voltage such that it is not charged again so that the new repetitions are no longer audible. It is known to avoid these disadvantages by subdividing the capacitor into two separate capacitors, one of which is shunted by a resistor so that the time constant of this part inclusive of the load resistance of the discharge circuit is small with respect to the time constant of the whole circuit arrangement comprising the series-combination of the two capacitors, one of which is shunted by a resistor.

If the two time constants are chosen so that the rapid repetitions are audible and the decay time of the tone is sufficiently long, the transition between the two discharge characteristics is not sufficiently smooth and becomes manifest in a disturbing manner.

According to the invention, this disadvantage is obviated by choosing the starting time constant of the discharge circuit to lie between 0.1 and 0.2 seconds and to have increased after half a second to two to four times the original value, the output voltage having decreased to 0.1 to 0.3 times the original value with the strongest key actuation.

In an embodiment of an electronic musical instrument according to the invention, in which the capacitor comprises the series-combination of two capacitors one of which is shunted by a resistor which is chosen so low that this capacitor has been discharged for the major part at the beginning of each repeated actuation, the other capacitor is shunted by an element the resistance of which increases with decreasing voltage.

Such an element may be constituted, for example, by a voltage-dependent resistor, a rectifier which may include a series resistor, etc. As a result, the time constant of the discharge circuit gradually varies and increases with decreasing capacitor voltage so that the sharp bend at the transition between the two discharge regions and the resulting click have disappeared.

In another embodiment of a musical instrument according to the invention having only one capacitor, this capacitor is shunted by an element the resistance of which increases with decreasing voltage.

In this circuit arrangement, a charging circuit including a rectifier element, the second capacitor and the resistor are economized. Although this circuit arrangement when compared with the known circuit arrangement has large advantages due to the disappearance of the click at the transition, it is difficult to cause the voltage of the capacitor after a strong actuation to decrease so rapidly that the weakest subsequent actuation is still audible.

While partly retaining the advantage of saving component parts, this disadvantage can be obviated in another embodiment of a musical instrument according to the invention, in which the capacitor is charged through a rectifier element by a coil in which upon actuation of a key a voltage is produced by means of a magnet connected to said key, which capacitor is also charged through the series-combination of a rectifier element and a resistor. The coil can be proportioned so that with the weakest actuation after a strong actuation the voltage is sufficiently high to recharge the capacitor so that the repetitions become audible.

In a favourable embodiment, the two coils are connected in series and are provided on the same magnetic circuit.

In another embodiment, the resistor connected in series with the rectifier element has a value of approximately five times the critical damping of the circuit comprising the inductance of the coil, the charging capacitor and the resistor itself. This results in a more or less linear relation between the intensity of actuation and the capacitor voltage.

The invention will now be described more fully with reference to the following FIGS. of which:

FIG. 1a shows a known circuit arrangement having a subdivided capacitor,

FIG. 1b shows the output voltage of this circuit arrangement as a function of time,

FIG. 2a shows such a circuit arrangement dependent elements,

FIG. 2b shows the output voltage of this circuit arrangement as a function of time,

FIG, 3 illustrates a circuit arrangement having one capacitor,

' FIG. 4a shows a circuit arrangement having one capacitor having voltageand two charging circuits, and

FIG. 4b shows for this circuit arrangement the relation between the actuation intensity and the capacitor voltage.

FIG. 1a shows the knowncircuit arrangement in which the charging capacitor is subdivided intotwo parts and comprises the series-combination of capacitors C, and C,. When the associated key is actuated, these capacitors are charged through rectifiers D, and 0,, respectively, by a voltage induced in the coils S, and S respectively, by means of magnets M, and M coupled with the same key.

The capacitor C is shunted by a resistor R which has a value such that the time constant r inclusive of the load resistance R is small with respect to the time constant 1, of the whole circuit arrangement. In order to permit of obtaining rapid weak repetitions after a strong actuation, the voltage of the series-combination of the capacitors C, and C must have been halved within the shortest possible repetition time and must then decrease comparatively slowly so that the capacitor C has been substantially completely discharged within the repetition time.

This is illustrated in FIG. lb in which the voltage is plotted as a function of time. The transition between the two rates of discharge is comparatively abrupt and becomes manifest in a disturbing manner. This disadvantage is obviated in the circuit arrangement of FIG. 2a by connecting a voltage-dependent resistance element comprising the series-combination of a diode D and a resistor R, in parallel with the capacitor C,. The starting time constant of the discharge circuit is again substantially equal to T and lies between 0.] and 0.2 seconds. After this period of time, C has been substantially completely discharged and V, continues to decrease due to the discharge of C, through the diode D and the resistor R,. Initially, the time constant thereof is mainly determined by the capacitance of C, and the value of resistor R,, i.e. as long as the voltage across the diode D exceeds the knee voltage. Subsequently, the diode is'slowly cut off and the resistance and hence the time constant r gradually increases until the series resistance of the diode D and the resistor R, approach the value infinite. The resistor R, and the diode D are proportioned so that after half a second the output voltage has decreased to 0.1 to 0.3 times the initial value with the strongest actuation. When the diode D is cut off, the time constant is again equal to 1-, of FIG. 1 which is determined by the value of the load resistor R and the capacitance of capacitor C,.

It will be appreciated that the series-combination of the diode D and the resistor R, may be replaced by an arbitrary element the resistance of which increases with decreasing voltage, such as, for example, a voltage-dependent resistor.

F IG. 3 shows the circuit arrangement of FIG. 2, in which, however, the charging circuit comprising the coil S the diode 0,, the capacitor C and the resistor R, has been omitted, while the values of capacitor C, and resistor R, are chosen to be slightly different.

This results in a considerable saving of components, but if with the components available the starting time constant cannot be chosen sufi'lciently low so that the voltage has not decreased sufficiently after 0.1 to 0.2 seconds to permit of obtaining rapid weak repetitions after the strongest actuation, the circuit arrangement of FIG. 4a provides a solution in which the saving of components can be partly retained and which consists in that S, is connected in series with a second coil S, in which, when the associated key is actuated, also a voltage is produced by a magnet connected to said key, which voltage also charges the capacitor C, through a series resistor R', and a rectifier element 0,. If with rapid weak repetitions the voltage across S, is not sufficient to charge the capacitor C,, this capacitor is charged through the series-combination of the coils S, and S whose voltage is sufficient. The ratio between the voltages V and V across the diodes D, and D, and hence the ratio between the currents i, through the diode D, and i, through the diode D, can be determined by the choice of resistor R,,.

It has been found that it is desirable for R to be chosen so that the maximum value of the current i is of the order of a quarter of that of the current i The ratio of the voltage e to the voltage e, is preferably chosen to be equal to 2 so that a weak repetition immediately after a strong actuation can become fully effective.

In a given embodiment of the circuit arrangement, with a strong actuation the no-load voltage across S, e, 7 v. and across S, S, e, e 21 v. If C, 16 J.f., V becomes= 3 v. and is substantially independent of R,. With a time constant 1-,

= C,R, of 0.2 second, the voltage of V, has decreased after 0.2

second to approximately one-third of 3 v. l v. If the weak repeated actuation is 0.1 times the strongest actuation, e, 0.7

proximately five times the critical damping L R 2 a of the circuit comprising the series-combination of the coils S, and S, and the capacitor C,.

It is claimed:

l. Aunit in a key operated musical instrument for providing a controlling voltage to a tone generator, comprising a coil, key operated magnet means for providing a magnetic field cutting the coil at a manually controlled rate, whereby a voltage having a manually controlled magnitude is generated in the coil, a capacitor, a diode, means for connecting the capacitor across the coil through the diode, whereby the capacitor is charged in proportion to the voltage generated in the coil, a voltage-controlled resistance element connected across the capacitor and having a gradually increasing resistance in response to decreasing voltage across the element, and means for connecting the resistance element to the tone generator.

2. A unit in a key operated musical instrument for providing a controlling voltage to a tone generator, comprising a first coil, a first key operated magnet means for providing a magnetic field cutting the coil at a manually controlled rate, a second coil, a second key operated magnet means mechanically connected to the first magnet means for providing an additional magnetic means cutting the second coil at a manually controlled rate, whereby a manually controlled voltage is simultaneously generated in both the first and the second coils, a first diode, a first ca acitor, means for connecting the first capacitor across the irst C011 through the first dlode,

means for connecting the first diode to one end of the second coil, a second diode connected to the other end of the second coil, circuit means for connecting the first capacitor to the other end of the second coil through the second diode, a voltage-controlled resistance element connected across the first capacitor and having a gradually increasing resistance in response to decreasing voltage across the element, and means for connecting the element to the tone generator through the circuit means.

3. A unit as claimed in claim 2, wherein the first coil is connected to the one end of the second coil through the first diode, and wherein the circuit means comprises a second capacitor and a resistor connected in parallel across the second diode and second coil and having a time constant in the range of 0.1 and 0.2 seconds.

4. A unit as claimed in claim 2, further comprising a resistor connected in series with the second diode and the second coil having sufficient resistance to limit the maximum current through the second diode to one fourth of the current through the first diode.

5. Apparatus as claimed in claim 2, further comprising a resistor connected in series with the second diode and the second coil and having a value approximately equal to five times the resistance necessary for the critical damping of a circuit comprising the first capacitor and an inductance equal to the sum of the inductance of the first and second coils. 

1. A unit in a key operated musical instrument for providing a controlling voltage to a tone generator, comprising a coil, key operated magnet means for providing a magnetic field cutting the coil at a manually controlled rate, whereby a voltage having a manually controlled magnitude is generated in the coil, a capacitor, a diode, means for connecting the capacitor across the coil through the diode, whereby the capacitor is charged in proportion to the voltage generated in the coil, a voltagecontrolled resistance element connected across the capacitor and having a gradually increasing resistance in response to decreasing voltage across the element, and means for connecting the resistance element to the tone generator.
 2. A unit in a key operated musical instrument for providing a controlling voltage to a tone generator, comprising a first coil, a first key operated magnet means for providing a magnetic field cutting the coil at a manually controlled rate, a second coil, a second key operated magnet means mechanically connected to the first magnet means for providing an additional magnetic means cutting the second coil at a manually controlled rate, whereby a manually controlled voltage is simultaneously generated in both the first and the second coils, a first diode, a first capacitor, means for connecting the first capacitor across the first coil through the first diode, means for connecting the first diode to one end of the second coil, a second diode connected to the other end of the second coil, circuit means for connecting the first capacitor to the other end of the second coil through the second diode, a voltage-controlled resistance element connected across the first capacitor and having a gradually increasing resistance in response to decreasing voltage across the element, and means for connecting the element to the tone generator through the circuit means.
 3. A unit as claimed in claim 2, wherein the first coil is connected to the one end of the second coil through the first diode, and wherein the circuit means comprises a second capacitor and a resistor connected in parallel across the second diode and second coil and having a time constant in the range of 0.1 and 0.2 seconds.
 4. A unit as claimed in claim 2, further comprising a resistor connected in series with the second diode and the second coil having sufficient resistance to limit the maximum current through the second diode to one fourth of the current through the first diode.
 5. Apparatus as claimed in claim 2, further comprising a resistor connected in series with the second diode and the second coil and having a value approximately equal to five times the resistance necessary for the critical damping of a circuit comprising the first capacitor and an inductance equal to the sum of the inductance of the first and second coils. 